Direct Current Cathode and Anode Effects and Changes in Handgrip Strength. Evaluation Through a Dynamometer Test: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Direct Current Cathode and Anode Effects and Changes in Handgrip Strength. Evaluation Through a Dynamometer Test (NCT02884427), a randomized na study. The primary outcome is Difference of Maximum Grip Strength.

2. Clinical Question

3. Trial Design

The registry record describes a randomized, controlled, triple-masked, parallel-group trial with enrollment of 150. The listed study status is completed. The start date is 2015-09, and primary completion is 2016-03. The phase is listed as NA. The sponsor is Quiropraxia y Equilibrio.

There were three groups: cathode stimulation, anode stimulation, and control. The posted primary-outcome summaries include 48 participants in the cathode group, 52 in the anode group, and 50 in control. These group counts sum to the recorded enrollment, but the registry record does not describe participant flow, exclusions, or whether every enrolled participant contributed to each outcome analysis. It also does not provide details of the randomization sequence, allocation concealment, or which parties were masked.

The intervention descriptions specify the electrode polarity and characterize the control as equipment installation without current delivery. The record does not report the stimulation settings, session duration, or additional treatment procedures. The study summary describes assessment of handgrip strength before and after the intervention in healthy subjects.

The primary outcome is a continuous measure of the difference in maximum grip strength, expressed in kilograms, with a mean and standard deviation reported for each group. The assessment timeframe is described as baseline and one hour later after one treatment session, assessed as up to one month. The registry record does not clarify that timeframe wording further. It lists sex-specific secondary outcomes for females and males, although posted results are available only for the female outcome. Reported analyses are not listed in the registry record.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Overall Study

5. Baseline Characteristics

The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.

6. Primary Endpoint

The registry lists the primary outcome as Difference of Maximum Grip Strength, measured over Baseline and 1 hours later (1 session of treatment), assessed as up to 1 month..

The primary endpoint is the change in maximum handgrip strength, measured in kilograms. For each participant, the recorded change was defined as the best result among the first three gripping attempts before the intervention compared with the best result among three attempts after it. The registry record describes the difference as the force change between pre-intervention and post-intervention testing.

Using the best of repeated attempts makes the endpoint a measure of the participant’s highest recorded grip force at each assessment, rather than the average of every attempt. Comparing the pre-intervention and post-intervention best results puts the focus on change over the session. The endpoint is continuous, so group summaries can describe both the average change and how variable individual changes were.

The stated assessment was at baseline and one hour later following one treatment session. The registry record also says the outcome was assessed as up to one month, without further clarifying this timeframe. The reported group means were 3.0 kg for cathode stimulation, 0.0 kg for anode stimulation, and -2.0 kg for control. The corresponding standard deviations were 5.0, 4.0, and 5.0 kg. Those summaries describe the posted results; the registry record does not give participant-level measurements or additional information about testing conditions.

7. Results Posted in the Registry

• Cathode Stimulation: mean 3.00 versus -2.00 on control; difference 5.00 (95% CI 3.02 to 6.98), standardized effect d = 1.00; z-test p = <0.001.
• Anode Stimulation: mean 0.00 versus -2.00 on control; difference 2.00 (95% CI 0.24 to 3.76), standardized effect d = 0.44; z-test p = 0.026.

8. Secondary Efficacy Endpoints

The registry also posts results for secondary outcomes. For each outcome below, the endpoint type, the test applied to the posted summary statistics, the result and its interpretation are given in turn. Secondary endpoints are usually not adjusted for multiple testing, so they support rather than confirm the primary finding.

Difference of Maximum Grip Strength for Females

• Endpoint type: Continuous: a mean value per participant, compared as a difference in means.
• Test: Unadjusted two-sample z-test for the difference in means, using the posted standard deviations.
• Result:
  • Cathode Stimulation: mean -0.30 versus -0.80 on control; difference 0.50 (95% CI -2.31 to 3.31), standardized effect d = 0.11; z-test p = 0.727.
  • Anode Stimulation: mean -0.80 versus -0.80 on control; difference 0.00 (95% CI -2.34 to 2.34), standardized effect d = 0.00; z-test p = 1.000.
• Interpretation:
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Cathode Stimulation and the control. The interval gives the range of effects that remain compatible with the data.
  • The 95% confidence interval includes no difference, so these data do not show a statistically significant difference between Anode Stimulation and the control. The interval gives the range of effects that remain compatible with the data.

The registry record lists sex-specific secondary outcomes for maximum grip-strength change in females and males. Posted results are available for the female outcome, but the male outcome results are not reported in the registry record. The female summaries show little separation in average change between the cathode, anode, and control groups compared with the overall primary summaries. The pairwise female comparisons are also imprecise, with confidence intervals that include zero.

This pattern does not establish that the primary and secondary results conflict. A subgroup outcome can differ from an overall outcome because it reflects a different set of participants and may be less precise. The female groups are smaller than the full primary groups, and the reported standard deviations show substantial variation relative to the female mean differences. The registry record does not state whether subgroup comparisons were planned or how they were intended to be interpreted.

The female comparisons are unadjusted recalculations from the posted group summaries, and the registry record lists no reported analyses. The record does not report a multiplicity procedure covering the primary and secondary outcomes or the several pairwise comparisons. When many outcomes or comparisons are examined, some apparently unusual results can occur by chance even if there is no underlying difference. This general concern means unadjusted secondary results should be treated as exploratory rather than as independent confirmation of the primary pattern.

Because male results are absent, the registry record does not support a complete comparison of the sex-specific outcomes. Nor does it provide a formal test of whether the results differ by sex. Separate summaries within a subgroup are not, by themselves, evidence that the treatment-group contrast differs between subgroups. The primary result remains the overall comparison specified as the primary outcome, while the posted secondary material gives only a partial and less conclusive view of subgroup patterns.

Secondary outcomes registered for this trial, for reference (only those above were recalculated):

• Difference of Maximum Grip Strength for Males
• Difference of Maximum Grip Strength for Females

9. Statistical Interpretation

10. Statistical Methods Explained

Handgrip change is a continuous outcome. A continuous measure can take values across a scale, here kilograms, and is commonly described using a mean and standard deviation. The mean represents the group’s average recorded change. The standard deviation describes how spread out individual changes are around that average. It is not the uncertainty in the mean itself: uncertainty in a group mean also depends on the number of observations and the variability among them.

In this trial, the endpoint is a within-participant difference between the best pre-intervention attempt and the best post-intervention attempt. The posted values summarize those differences by group. A positive group mean indicates that the average recorded change was positive under the endpoint’s stated direction; a negative mean indicates an average change in the opposite direction. The interpretation depends on the endpoint definition and the order in which the pre- and post-intervention values are subtracted. The record describes the comparison but does not give participant-level values.

The pairwise mean difference compares the average change in a stimulation group with the average change in control. For cathode stimulation, the posted summaries yield an unadjusted mean difference of 5.0 kg. For anode stimulation, the corresponding difference is 2.0 kg. These are unadjusted recalculations from group summary statistics. They are not identified as formal reported analyses in the registry record, which lists no reported analyses. As the registry record does not state the original analysis plan, these recalculations should not be assumed to reproduce an intended sponsor analysis.

What does a confidence interval describe?

A confidence interval gives a range of values compatible with the observed data under the method used to calculate it. Its width conveys precision: a narrower interval indicates a more precise estimate, while a wider interval indicates greater uncertainty. A confidence interval is not a guarantee that the true value lies in the particular interval, nor does it describe the range of individual participant outcomes. The reported intervals for the primary comparisons are calculated from the posted summaries.

A p-value evaluates how incompatible the observed data are with a specified null hypothesis under the assumptions of the test. It is not the probability that the null hypothesis is true, and it does not measure the size or practical importance of a difference. The primary comparison p-values are unadjusted. Because the registry record does not list the trial’s reported analyses or statistical plan, the tests shown should be interpreted as unadjusted recalculations rather than as a documented original analysis.

Why can variability matter?

Standard deviation is relevant both to interpretation and to planning. Greater variation among participant changes makes a group average less precise when sample size is held fixed. If continuous outcomes have more variability than a statistical model expects, the data may be over-dispersed relative to that model; standard errors can then be too small if the extra variability is ignored. This is a general statistical point. The posted group standard deviations describe observed spread, but the registry record does not report a specific model, a check for over-dispersion, or an adjustment for it.

The planning illustrations use a normal approximation, equal allocation between the two arms being compared, and a two-sided significance level of 0.05. For those illustrations, the effect to detect is defined as a stated fraction of the observed effect. These are planning assumptions for the illustrations, not evidence about the assumptions used when the trial was designed. The trial’s own original sample-size justification is not reported in the registry record.

The illustrations are pairwise and do not account for every design feature that might affect a trial’s actual sample-size needs. For example, the record does not report an allowance for missing outcomes or a multiplicity adjustment. The planning values are not observed power and should not be interpreted as a retrospective probability that the trial detected an effect. They are estimates of participants per arm under the stated planning assumptions.

Randomization is intended to make assigned groups comparable, on average, with respect to factors that could affect outcomes. The registry record says allocation was randomized, but does not report how the sequence was generated or concealed. Triple masking is listed, but the record does not specify which parties were masked or how masking was maintained. Those missing design details limit assessment of how well randomization and masking were implemented.

Finally, the registry outcome summaries do not show participant-level data, missingness patterns, or the handling of incomplete observations. Those details matter because analyses based only on observed outcomes can be affected if missingness is related to participant characteristics or outcome values. The registry record does not report an analysis population, missing-data method, or sensitivity analysis. These are limits on what can be inferred from the posted statistical summaries, not proof that a particular problem occurred.

11. Confidence Intervals and Precision

Precision concerns how tightly an estimate is determined by the data and calculation method. The primary pairwise estimates are 5.0 kg for cathode stimulation versus control and 2.0 kg for anode stimulation versus control. Their 95% confidence intervals are 3.02 to 6.98 kg and 0.238 to 3.761 kg, respectively. The intervals quantify uncertainty in the estimated group differences; they do not describe the distribution of changes among individuals.

The cathode comparison’s interval spans values above zero, as does the anode comparison’s interval. The widths differ, reflecting the estimates and uncertainty associated with each comparison. The anode interval extends closer to zero, so its lower end is compatible with a smaller positive difference than the cathode interval’s lower end. Neither interval alone establishes practical importance. The registry record does not identify a threshold for a meaningful change in grip strength.

The group standard deviations—5.0 kg for cathode, 4.0 kg for anode, and 5.0 kg for control—show that participant changes varied within each group. The confidence intervals concern group mean differences, not individual variation. The reported group sizes are 48, 52, and 50, respectively; however, the record does not describe missing outcome data or whether the group counts represent all participants in the analysis.

These intervals are based on unadjusted recalculations from the posted summary statistics. The registry record does not list formal reported analyses, the original statistical plan, or any adjustment for multiple comparisons. Thus, the intervals convey precision under the calculation used, not all possible uncertainty arising from trial conduct, analysis choices, or incomplete reporting.

12. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning illustrations give participants per arm for comparisons between a stimulation group and control; they are not totals across all arms. The reported assumptions are a two-sided significance level of 0.05, equal allocation between the two arms, and a normal approximation. The effect used for planning is a stated fraction of the observed effect. The trial’s own original design assumptions and sample-size justification are not reported in the registry record.

The 80% power column estimates the participants per arm needed for an 80% chance of detecting the specified effect under those planning assumptions, if that effect is the true difference. The 90% power column gives the corresponding planning estimate for a higher target chance of detection. These are planning calculations, not guarantees about a future study’s results. The displayed values for each effect fraction apply separately to the cathode-versus-control and anode-versus-control comparisons.

The rows planning for 100%, 75%, and 50% of the observed effect illustrate how the assumed effect size changes the participant requirement. A smaller effect is harder to distinguish from random variation and therefore requires more participants under the same assumptions. The illustrations use the observed effect as their reference; a future study may have a different true effect, variability, or analysis plan.

These figures are not observed power. They are planning illustrations based on stated assumptions, rather than a retrospective measure of how likely the completed trial was to find an effect. The registry record does not report the sample-size justification used for the original trial.

13. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, Δ is the difference in means to detect and σ is the common standard deviation.

Worked calculation for this trial

1. Observed difference Δ = 5.000; pooled standard deviation σ = 5.000.
2. n = 2 × (1.96 + 0.842)² × 5.000² / 5.000² = 15.7, rounded up to 16 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
delta <- 5                      # observed difference in means
sigma <- 5                     # pooled standard deviation
n_per_arm <- function(power, frac = 1) {
  ceiling(round(2 * (z_a + qnorm(power))^2 * sigma^2 / (delta * frac)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (t-based, so very slightly larger)
cat("power.t.test:", round(power.t.test(delta = delta, sd = sigma, power = 0.80)$n, 1), "\n")

# Simulation: exact two-sample t-test using simulated means and variances
set.seed(2884427)
n    <- n_per_arm(0.80)
reps <- 20000
m_diff <- rnorm(reps, delta, sigma * sqrt(2 / n))             # difference in sample means
s2     <- sigma^2 * rchisq(reps, 2 * (n - 1)) / (2 * (n - 1))   # pooled sample variance
tstat  <- m_diff / sqrt(s2 * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(tstat) > qt(0.975, 2 * (n - 1))), reps))

Output from running the code

100% of observed effect: n per arm = 16 (80% power), 22 (90% power)
 75% of observed effect: n per arm = 28 (80% power), 38 (90% power)
 50% of observed effect: n per arm = 63 (80% power), 85 (90% power)
power.t.test: 16.7 
Simulated power at n = 16 per arm: 0.780 (20000 replicates)

The simulation draws many sets of group means and variances at the planned sample size and counts how often the two-sample t-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

14. Multiplicity, Missing Data and Analysis Populations

The registry record lists one primary outcome and two sex-specific secondary outcomes, but it does not report the statistical plan or a procedure for handling multiplicity. The pairwise comparisons in the posted results are unadjusted recalculations from summary statistics. The record does not say whether the original investigators adjusted for testing multiple groups, outcomes, or subgroups.

Multiplicity is a general statistical concern when several hypotheses are tested. Each additional test creates another opportunity for a result that appears notable by chance. Adjustment methods can change the threshold for interpreting evidence or the reported uncertainty. Without a reported plan, it is not possible to determine whether the posted pairwise p-values and confidence intervals reflect the intended approach to multiple comparisons. They should be read as unadjusted results rather than as evidence that multiplicity was addressed.

Missing-data handling is also not described. The record posts primary group counts and female subgroup counts, but does not provide participant flow, the number with missing outcome measurements, reasons for missingness, or a method for dealing with incomplete observations. It is therefore not possible to determine whether every randomized participant contributed data or whether analyses were restricted to participants with observed outcomes.

The analysis population is not specified. The registry record does not say whether the results are based on all randomized participants, participants who received the assigned procedure, or another defined group. It also does not report sensitivity analyses that might assess the consequences of missing data or different analysis populations. This absence of reporting does not show that missing data or analysis-population issues occurred; it means their effects cannot be assessed from the registry record.

Reported analyses are not listed. As a result, the posted summary statistics and recalculated comparisons cannot be matched to a documented analysis plan or verified against a reported sponsor analysis. The registry record also does not describe interim analyses, stopping rules, or other planned statistical decisions. These details are not reported in the registry record.

15. What the Result Does, and Does Not, Mean

The posted results describe changes in handgrip strength after a single session in the three randomized groups. The overall group means were higher for cathode stimulation and anode stimulation than for control, and the unadjusted pairwise recalculations estimate positive mean differences versus control. Their confidence intervals quantify uncertainty under the calculation used. This is a statistical description of the registry results, not a claim about clinical benefit.

The estimates do not show that every participant in a stimulation group increased grip strength, or that each participant in control had a decrease. Group means can conceal substantial variation, and the posted standard deviations indicate spread in individual changes. No threshold for a clinically or practically important difference is reported, so the size of the observed differences cannot be classified as meaningful or unimportant on that basis.

The result is limited to the outcome and assessment described: maximum grip-strength change measured in kilograms before and after one treatment session, with the assessment stated as baseline and one hour later and also described as assessed as up to one month. The registry record does not clarify this timeframe further. It does not provide evidence about effects over longer periods, repeated sessions, or outcomes beyond handgrip strength.

The record describes healthy subjects, but detailed eligibility criteria and participant characteristics are not reported. This limits conclusions about whether the results apply to other populations. The registry record also does not report a full statistical analysis plan, participant flow, missing-data handling, or formal reported analyses. The pairwise p-values and confidence intervals are unadjusted recalculations from posted group summaries; they are not evidence of a documented adjustment for multiple comparisons.

In short, the posted data show group-level differences in short-term mean change, with uncertainty quantified by the reported intervals. They do not establish the mechanism behind any differences, determine practical importance, or settle how results would generalize beyond the study population and measurement conditions. Those questions require information not reported in the registry record.

16. Why This Trial Matters Statistically

This trial illustrates why a group mean alone is not a complete description of a continuous clinical outcome. The reported mean changes are accompanied by standard deviations, which show that participant changes varied within each arm. Pairwise estimates and confidence intervals add a comparison with control and indicate how precisely those average differences are estimated under the calculation used.

It also demonstrates the distinction between a registry’s posted summaries and a reported statistical analysis. The registry lists no reported analyses, while the pairwise estimates and p-values can be recalculated from the group summaries. Labeling those comparisons as unadjusted recalculations helps distinguish them from a prespecified or sponsor-reported analysis. That distinction matters when the statistical plan and multiplicity approach are not described.

The sex-specific secondary outcome underscores the importance of complete outcome reporting. Female results are posted, while male results are not reported in the registry record. Without complete subgroup results and a reported interaction analysis, separate subgroup summaries cannot establish whether the treatment contrasts differ between sexes.

Finally, the sample-size illustrations show how planning depends on assumptions about the effect to detect, target power, and allocation. They are not a retrospective evaluation of the completed trial’s success. The original sample-size justification is not reported, so the planning illustrations should not be confused with the design rationale. Taken together, these points make the record useful for understanding statistical interpretation while also showing why transparent analysis plans and complete reporting are essential.

17. Limitations

• The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
• Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.

Several trial-specific details needed to assess the results are not reported in the registry record. Although the study is described as randomized and triple-masked, the record does not specify sequence generation, allocation concealment, which parties were masked, or how masking was maintained. It also does not report stimulation settings, session duration, or further procedural details for the control condition.

The population description refers to healthy subjects, but eligibility criteria, recruitment methods, and participant characteristics are not provided. Participant flow and outcome availability are also unclear. Although enrollment is 150 and the primary group summaries include 48, 52, and 50 participants, the record does not state whether these were all randomized participants or explain any exclusions or missing measurements.

The assessment timeframe is described as baseline and one hour later after one treatment session, assessed as up to one month. The record does not explain the wording further. The available results therefore should be interpreted as short-term findings in the context of the stated single-session assessment, without assuming a longer follow-up.

The registry record lists no reported analyses and does not provide the original statistical plan, missing-data method, analysis population, multiplicity procedure, or sample-size justification. Pairwise estimates and p-values are unadjusted recalculations from group summaries. Female secondary results are posted, but male secondary results are not reported in the registry record. Adverse-event fields list zero participants at risk and zero affected in each group, while deaths are not reported; those entries do not establish that no adverse events occurred. These reporting limitations restrict how fully the results and safety reporting can be assessed.

18. Related Tutorials

19. Related Statistical Calculators

20. Sources

• ClinicalTrials.gov: Direct Current Cathode and Anode Effects and Changes in Handgrip Strength. Evaluation Through a Dynamometer Test — NCT02884427.
• Registry record last updated 2018-10-09; status last verified 2018-09.
• Results first posted 2017-07-14.
• Data retrieved from ClinicalTrials.gov on 2026-11-09.
• Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.

21. Record Summary

NCT02884427 is a completed randomized, controlled, triple-masked, parallel-group trial sponsored by Quiropraxia y Equilibrio, with enrollment of 150. It compared cathode stimulation and anode stimulation with a control procedure in healthy subjects. The primary outcome was change in maximum grip strength in kilograms, assessed before and after one treatment session.

The posted primary group means were 3.0 kg for cathode stimulation, 0.0 kg for anode stimulation, and -2.0 kg for control. Unadjusted recalculations from those summaries estimate mean differences versus control of 5.0 kg and 2.0 kg, respectively. The registry record lists no reported analyses. Female secondary results are posted; male secondary results are not reported in the registry record. Important details about the original analysis plan, missing data, and sample-size justification are not reported.